Controlled therapeutic trials and natural history surveys are being conducted by the International Study of Kidney Disease in Children in which 27 clinics in 11 countries are participating (13 in the U.S., 3 in England, 2 in Germany, one each in Brazil, Canada, Finland, Holland, Mexico, Scotland, Switzerland, and Spain). The natural history of the nephrotic syndrome in 521 children all of whom had renal biopsies at the time of diagnosis is being studied. Over 80 percent of these children have been followed from 3 to 10.4 years and follow-up studies will be continued. Therapeutic trials and natural history studies are in progress on azathioprine in lupus nephritis, cyclophosphamide in anaphylactoid purpura and focal segmental glomerulosclerosis, and prednisone in membranoproliferative glomerulonephritis. The role of the coagulation system in rapidly progressive glomerulonephritis will be evaluated in a trial in which the contrast group will receive azathioprine, cyclophosphamide and prednisone and the experimental group will receive these drugs in addition to dipyridamol and heparin followed by warfarin.